1. Technical Field
The present invention relates generally to surgical instruments and more specifically to torque-indicating drivers.
2. Background Information
In some surgical procedures, a surgeon may need to exert torque on a fastener or other object disposed within the human body. For example, orthopedists often treat a variety of different types of bone fractures and other skeletal conditions by installing bone screws in an affected area, to stabilize a bone, to attach constructs to a bone, or for other therapeutic purposes. When installing a bone screw into a bone, it is important that excessive torque not be applied. Excessive torque may “strip” threads in a bone, or may damage the bone screw itself. Certain bone screws that are made from easily deformable bioabsorbable materials may be particularly susceptible to damage. Due to the potential complications that can result from damaged caused from excessive torque, it is quite important that a surgeon measure the amount of torque he or she applies.
A variety of different types of torque-indicating drivers exist for applying measured amounts of torque. Some torque-indicating drivers employ a torsion rod. In such drivers, the torsion rod is generally coupled at one end to a bit that engages a load, and at the other end to a handle where torque is applied. Applied torque is transmitted to the bit via the torsion rod, which angularly deflects in response to the torque. The deflection of the torsion rod is measured by comparing markings on the torsion rod with marking on the handle.
While torsion rod-based torque-indicating drivers are relatively simple and easy to manufacture, they suffer some shortcomings. For example, they are often unsuited for high-torque applications, as many torsion rods may not withstand such torque levels, or may not accurately measure torque at such torque levels. High torque levels may be needed for certain types of fasteners used in some surgical procedures.
Other types of existing torque-indicating drivers may employ one or more substantially rectangular plate springs, or one or more helical springs, rather than a torsion rod. Angular deflection of the springs is measured with markings, similar to in torsion rod-based designs. While plate springs and helical springs are often capable of withstanding higher levels of torque than torsion rods, they typically add bulk and thickness to the shaft of a torque-indicating driver. Accordingly, torque-indicating drivers that employ springs are generally unsuitable for use in confined spaces, for example, in the confined surgical space of a minimally invasive surgical procedure.
Further, existing torque-indicating drivers do not always well indicate the amount of torque that is applied. As discussed above, such instruments generally rely on indicator markings. Such markings are typically only visible from a certain perspective, for example, from directly above the driver, or from the side of the driver. During a surgical procedure, it may be difficult for a surgeon position him or herself in the best viewing location to view the markings. In some cases, sight lines may be obstructed by other instruments, or other medical personnel involved in the procedure, thus making it difficult to view the markings and measure the torque that is being applied.
Further, it is often difficult to adjust or calibrate many existing torque-indicating drivers during manufacture. Small variations may exist in the torsional properties of the components of a driver. Therefore, it may be desirable to make adjustments to a driver before it is delivered to a customer, to ensure it accurately measures torque. However, many existing drivers lack a simply yet effective mechanism for making such adjustments.
Accordingly, there is a need for an improved torque-indicating driver that overcomes the shortcoming of prior designs.